Systems and methods for deploying a biosensor in conjunction with a prosthesis

ABSTRACT

A biosensor for monitoring pressure or other physical parameters at an aneurysm site is mountable to a tubular prosthesis that is expandable between contracted and enlarged conditions. A loop, having the biosensor attached thereto, is securable around the prosthesis. An apparatus is used to deliver the loop to an aneurysm site that includes a catheter having a connector on its distal end for detachably securing the loop thereto. The prosthesis is advanced in a contracted state to the aneurysm, and the apparatus, with the loop connected thereto, is advanced to the aneurysm site. The loop and the prosthesis are positioned coaxially with respect to one another, and the prosthesis is expanded towards its enlarged condition, thereby engaging the loop around the prosthesis and engaging the prosthesis with a wall of the blood vessel at the treatment site.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical devicesfor monitoring internal physiological conditions of a patient, and, moreparticularly, to a biosensor that is attachable to a prosthesis forremotely monitoring physiological conditions of a patient, such aspressure within an aneurysm cavity across which a prosthesis isimplanted.

BACKGROUND

An aneurysm is a weakening of a wall of a blood vessel that generallyresults in a ballooning of the wall, and, if left untreated, may resultin a rupture that may seriously threaten the life of a patient. Theweakening of the wall may be due to injury, infection, or otherconditions, such as a congenital defect in the arterial connectivetissue. Common forms of such an aneurysm include an abdominal aorticaneurysm (“AAA”), an iliac aneurysm, a bifurcated aneurysm of theabdominal aorta and one or both of the iliac arteries, and a thoracicaortic aneurysm.

To treat a patient suffering from an aneurysm, a tubular prostheticgraft may be implanted across the aneurysm using an open surgicaltechnique to substantially isolate the weakened region of the vesselfrom adjacent healthy regions. For example, the vessel wall may be cutlongitudinally along the vessel wall, the graft inserted and anastomosedcoaxially within the vessel as an internal replacement for the diseasedsegment, and then the longitudinal cut may be sutured closed.Alternatively, opposite ends of a prosthetic graft may be sutured to avessel on either side of the weakened region to form a bypass conduitaround the diseased segment. Such surgical approaches, however, mayinvolve extensive recovery times, may be complicated because of thedifficulties in suturing the graft to the vessel, and/or may beunsuitable for many at-risk patients because of the high mortality andmorbidity rates associated with a surgical intervention of thismagnitude.

As an alternative to open surgery, endolumenal stent graft implantationhas been suggested. An endolumenal stent graft generally includes avascular graft and a support structure, such as a self-expanding orballoon-expandable stent, that may engage each end of the graft or mayextend along all or a portion of a length of the graft. The stent graftmay be introduced percutaneously into the patient's vasculature in areduced profile, for example, on or in a delivery catheter. The stentgraft may be advanced to a treatment site, such as a damaged segment ofthe abdominal aorta, and placed across the treatment site. The supportstructure may then be radially expanded, anchoring the graft to thehealthy regions of the vessel adjacent the damaged segment, andsubstantially sealing the aneurysm from the rest of the circulatorysystem. As a result, pressure within the isolated aneurysmal sac may bereduced, thereby reducing stress or “endotension” on the weakened wallof the vessel. Endotension is a physical parameter that may indicate thelikelihood of an aneurysm rupturing, and is generally defined in termsof the internal pressure within the aneurysm, the aneurysm diameter andvessel wall thickness.

One potential complication that may occur after a stent graft isimplanted is the formation of an endoleak. Endoleaks may be divided intofour categories: leakage due to improper sealing of the graft againstthe vessel wall (Type I), blood flow into the aneurysmal sac throughbypass arteries (Type II), leakage due to mechanical failure of thegraft system (Type III), and leakage through the graft due to theporosity of the graft material (Type IV).

If fluid leaks into the aneurysmal sac, it may increase the pressure orendotension within the aneurysm, possibly resulting in an aneurysmalrupture. To substantially reduce the risk of this occurring, earlydetection of endoleaks or endotension may be important. With earlydetection, the pressure within the aneurysmal sac may be reduced bysubsequent endovascular treatment (for example, further expansion of thestent graft support structure, or additional stent graft implantation toimprove sealing), or, if necessary, surgical intervention.

Currently, contrast-enhanced computerized tomography (CT) is often usedto detect endoleaks, which relies on x-ray imaging of an abdominalregion after injection of a contrast media. If an endoleak is present,the aneurysmal sac may fill with contrast media and the endoleak maythen be identified by the CT scan. Although CT scans are considered areliable method for detecting endoleaks, they require an experiencedoperator and an expensive apparatus, placing significant financialconstraints on its frequency of use. In addition, a CT scan procedureexposes the patient to x-ray radiation, and thus may only be recommendedevery 3 to 6 months following stent graft implantation. Finally, becauseCT scans only detect actual leakage and not pressure within theaneurysm, they may not detect small leaks that may cause slow, butpotentially dangerous, pressurization within the aneurysm.

As an alternative to CT scans, ultrasound imaging may be used to detectendoleaks. Ultrasound imaging uses a simpler apparatus, resulting in apotential cost savings over CT scanning, and does not involve the use ofionizing radiation and its associated risks. The quality of ultrasoundimaging, however, may be more operator dependent, and therefore may beless reliable than CT scans.

Accordingly, it is believed that a system and method for monitoringinternal pressure within an aneurysmal sac may be considered useful.

SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods forimplanting a biosensor, preferably in conjunction with anendoprosthesis, within an abdominal aortic aneurysm or other enlarged orweakened treatment site within a body lumen of a patient.

In accordance with a first aspect of the invention, an apparatus formonitoring a physical parameter at a treatment site within a body lumenis provided. The apparatus includes a tubular prosthesis expandablebetween a contracted condition for facilitating introduction into thebody lumen, and an enlarged condition for contacting a wall of the bodylumen at the treatment site. A substantially enclosed loop having a sizefor substantially securing the loop around the prosthesis in itsenlarged condition is provided with a biosensor attached to the loop.

In one preferred embodiment, the loop may be a ring or sleeve formedfrom a substantially elastic material, the ring or sleeve having arelaxed state having a cross-section smaller than the prosthesis in itsenlarged condition. In an alternate preferred embodiment, the loop maybe a substantially inelastic, flexible thread having a cross-sectionsimilar to the prosthesis in its enlarged condition.

In accordance with another aspect of the invention, an apparatus isprovided for delivering the biosensor device to a treatment site withina body lumen. The apparatus includes an elongate member having aproximal end and a distal end adapted for introduction into the bodylumen, and a connector located on the distal end of the elongate memberfor detachably securing the loop to the distal end of the elongatemember. Preferably, an actuator is provided on a proximal end of theelongate member for detaching the loop from the connector. In preferredembodiments, the apparatus may also include a sheath slidable over theelongate member or other constraint for constraining the loop tofacilitate its introduction into the body lumen.

By way of example, in one preferred embodiment, the connector is a wirehaving a first end extending from the proximal end of the elongatemember, and a second end extending to the distal end of the elongatemember. The wire may be intertwined with the loop to therebysubstantially secure the loop to the distal end of the elongate member.The actuator preferably is a handle on the first end of the wire forpulling the second end of the wire from the distal end towards theproximal end, thereby releasing the loop therefrom. The loop may includea ring for receiving the wire therethrough.

In accordance with still another aspect of the invention, a deliverydevice is provided for directing the prosthesis to the treatment site inits contracted condition. The delivery device preferably has across-section substantially smaller than a cross-section of the loop,thereby facilitating positioning the loop coaxially with respect to theprosthesis before the prosthesis is deployed from the delivery device.

In accordance with yet another aspect of the invention, a method isprovided for implanting a biosensor at a treatment site within a bodylumen. In a preferred implementation, a tubular prosthesis is advancedin a contracted state within the body lumen to the treatment site, forexample, mounted to a delivery device. A loop is also advanced to thetreatment site, the loop including a biosensor attached thereto.Preferably, the loop is detachably connected to a delivery apparatusthat is used to advance the loop to the treatment site. The loop may bedeployed from a compressed state on the delivery apparatus once advancedto the treatment site, and manipulated to assume an open configurationacross the treatment site.

In one preferred embodiment, the loop may be expanded across thetreatment site before the prosthesis is advanced to the treatment site,and the prosthesis may be advanced through the loop upon advancement ofthe prosthesis to the treatment site. Alternatively, the loop may beadvanced coaxially over the delivery device to the treatment site.

Preferably, the loop and the prosthesis may be positioned coaxially withrespect to one another at the treatment site. The prosthesis may then beexpanded towards an enlarged condition, thereby substantially engagingthe loop around the prosthesis and substantially engaging the prosthesisto a wall of the blood vessel at the treatment site. Once the prosthesisis expanded, the loop may be released from the delivery apparatus, andthe apparatus withdrawn from the patient. As a result, the biosensor isdisposed within an aneurysmal sac at least partially defined by theaneurysm. The biosensor may then be used to remotely monitor theaneurysmal sac to detect pressure, leaks or other desired physicalconditions therein.

Other objects and features of the present invention will become apparentfrom consideration of the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a preferred embodiment of a biosensorattached to a flexible band.

FIGS. 2A and 2B are perspective views of a stent graft in a contractedand an expanded condition, respectively, with the biosensor of FIG. 1disposed therearound.

FIG. 3 is a side view of a preferred embodiment of an apparatus fordelivering a biosensor device detachably secured to the apparatus by awire connector.

FIGS. 4A-4D are cross-sectional views of an abdominal aortic aneurysm,showing the implantation of a stent graft across the aneurysm with abiosensor mounted thereon that is disposed within the aneurysmal sac.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, FIG. 1 shows a first preferred embodimentof a biosensor device 10 that includes a loop or lasso 12, preferably asubstantially enclosed band of material, to which a biosensor 14 isattached. The biosensor 14 may be attached to the loop 12 by any knownmethod, such as with sutures, adhesives, sonic welding, and the like.The biosensor 14 may be used to remotely measure one or more physicalparameters within a patient's body.

For example, the biosensor 14 may be a pressure sensor, a temperaturesensor, a pH sensor, a blood sugar sensor, a blood oxygen sensor, amotion sensor, a flow sensor, a velocity sensor, an acceleration sensor,a force sensor, a strain sensor, an acoustics sensor, a moisture sensor,an osmolarity sensor, a light sensor, a turbidity sensor, a radiationsensor, an electromagnetic field sensor, a chemical sensor, an ionicsensor, and an enzymatic sensor.

In preferred embodiments, the biosensor 14 employs wireless telemetry todeliver information from the implantation site to an instrument externalto the body. Further, the biosensor may or may not require a battery.For example, one preferred biosensor 14 is constructed in accordancewith the teachings of U.S. patent application Ser. No. 09/303,644, whichis fully incorporated by reference for all that it teaches anddiscloses. As taught therein, an acoustic telemetry biosensor includesmeans for converting acoustic energy received from an externallyoriginated interrogation signal into a current supply for powering oneor more sensors embedded in the biosensor for measuring variousbiological parameters at the implantation site. The biosensor 14 furtherpreferably includes means for modulating the interrogation signal totransmit the measured information external to the body.

In another preferred embodiment, the biosensor 14 is constructed inaccordance with the teachings of U.S. Pat. No. 5,704,352, which is alsofully incorporated by reference for all that it teaches and discloses.Other biosensor constructions are also possible and will be known tothose skilled in the art.

Turning to FIGS. 1, 2A, and 2B, the loop 12 has a predeterminedcross-section for substantially engaging a prosthesis 20 in its enlargedprofile (FIG. 2B). The prosthesis is preferably a stent graft includinga tubular prosthetic graft 22 supported by a support structure 24. Thegraft 22 may be provided from a substantially non-porous bio-compatiblematerial, such as Dacron or ePTFE, that is formed into a tubular shape.The material is substantially flexible, thereby allowing the graft 22 tobe rolled or folded into a reduced profile, accommodating deliverythrough tortuous anatomy, and/or facilitating implantation within curvedblood vessels.

The support structure 24 is preferably a tubular stent that extendsalong an inside surface of the graft 22 for substantially the entirelength of the graft 22. The support structure 24 may be attached to thegraft 22 in a variety of ways, such as by sutures, wires, sonic welding,adhesives, and the like, as is well known in the art.

In an alternative embodiment, the support structure 24 may be attachedto an outer surface of the graft (not shown), or may be woven into thegraft material (also not shown). In a further alternative, a pair ofstents (not shown) may be provided that may be attached to respectiveend regions of the graft 22, with an intermediate region of the graft 22being unsupported.

The support structure 24 is radially expandable between a contractedcondition (FIG. 2A) for facilitating introduction into a patient'svasculature, and an enlarged condition (FIG. 2B) for substantiallyengaging the wall of a blood vessel. In one embodiment, the supportstructure 24 may be a self-expanding stent, i.e., that is biased towardsits enlarged condition but may be compressed and/or constrained in itscontracted condition during delivery. Alternatively, the supportstructure 24 may be a plastically-deformable stent, i.e., that remainsin its contracted condition until it is forcibly expanded to assume itsenlarged condition, for example, using a balloon.

In one preferred embodiment, the loop 12 is formed from a substantiallyelastic material, such as silicon or polyurethane. The loop 12preferably has a relaxed state having a cross-section substantiallysmaller than the prosthesis 20 in its enlarged condition, for example,25-50% smaller. Preferably, the elastic material has an elasticity suchthat the loop 12 applies a radially inward pressure against theprosthesis 20 that is sufficiently strong to substantially secure theloop 12 to the prosthesis 20 in its enlarged condition without deformingor damaging the prosthesis 20. For example, the loop 12 may impose apressure that is less than the anticipated internal pressure experiencedwithin a body lumen, whereby the internal pressure may counteract theinward pressure imposed by the loop 12. Preferably, the loop 12 imposesan inward pressure of between about 5-60 mm Hg against the prosthesis inits enlarged condition.

In alternate preferred embodiments (not shown), the loop 12 may beformed from a substantially inelastic, flexible thread or band ofmaterial having a cross-section similar to the prosthesis 20 in itsenlarged condition. Preferably, the loop 12 has a cross-section about5-30 percent larger than a cross-section of the prosthesis 20 in itsenlarged condition. Alternatively, the loop 12 may be semi-rigid and mayhave a “C” shape (not shown) allowing it to be secured around theprosthesis 20 when the prosthesis 20 is expanded. In a still furtheralternative embodiment, the loop 12 may include an inelastic portion andan elastic portion (not shown).

The loop 12 may be substantially flexible and limp, or alternatively,may be biased to assume a substantially circular, open configuration.For example, the loop 12 may be formed from a shape memory orsuperelastic alloy, such as a nickel-titanium (“Nitinol™”) alloy. Thus,the loop 12 may be compressed, wrapped, or coiled into a compressedstate to facilitate its introduction into a patient's vasculature, butmay automatically expand to its open configuration upon release at atreatment site where the device 10 is to be implanted.

Turning to FIG. 3, an apparatus 50 is shown for delivering the biosensordevice 10 within a body lumen of a patient. The apparatus 50 includes aflexible catheter 52 or other elongate member, having a proximal end 54and a distal end 56 having a size and shape for facilitating insertioninto a patient's vasculature. The catheter 52 may have a guidewire lumen58 to facilitate advancement of the catheter 52 over a guidewire 80, asis known in the art.

The catheter 52 preferably includes first and second lumens 60, 62 thatextend between the proximal and distal ends 54, 56. A wire 64, forexample, made of nylon or other flexible, low friction material, may beslidably inserted into the lumens 60, 62 such that first and second ends66, 68 of the wire 64 extend from the proximal end 54 and anintermediate portion 70 forms a looped connector that extends from thedistal end 56. The first end 66 is provided loose, while the second end68 preferably includes a handle 69.

The loop 12 may be received in the intermediate portion 70 forsubstantially securing the biosensor device 10 to the distal end 56 ofthe catheter 52. For example, during assembly, the first end 66 of thewire 64 may be inserted distally into the first lumen 60 from theproximal end 54 of the catheter 52 until it extends from the distal end56 (not shown). The wire 64 may then be intertwined through the loop 12,preferably through a ring 18 attached to the loop 12, and insertedproximally into the second lumen 62, possibly until the first end 66extends from the proximal end 56 of the catheter 52. Alternatively, thewire 64 may be intertwined through a hole in the biosensor device 10.

When it is desired to disconnect the biosensor device 10 from thecatheter 52, the handle 69 may be pulled until the first end 66 of thewire 64 is pulled from the second lumen 62 and enters the first lumen60, thereby releasing the loop 12 from the wire 64. Thus, the wire 64provides a connector for securing the biosensor device 10 to thecatheter 52, and the handle 69 provides an actuator for releasing thebiosensor device 10 that may be activated from the proximal end 54 ofthe catheter 52. If additional protection of the biosensor device 10 isdesired, an overlying sheath (not shown) may be provided that isslidable over the catheter 52 from the proximal end 54 to the distal end56. A locking mechanism may be included to prevent the unintentionaldetachment of the biosensor device 10.

The biosensor device 10 may be received in a lumen of the sheath, forexample, simply by advancing the sheath distally over the biosensordevice 10, or by compressing the loop 12 and inserting the compressedbiosensor device 10 into the sheath.

In an alternative embodiment, the first and second lumens 60, 62 mayterminate proximate to the distal end 56, thereby securing the biosensordevice 10 to a side region of the catheter 52 (not shown). If desired,the loop 12 may then be wound around the catheter 52 and constrainedthereon, for example, by an overlying sheath (not shown).

In a further alternate embodiment, a different connector may be providedon the distal end 56 of the catheter 52, such as a pair of opposingmandibles (not shown) having a slot therebetween for engaging the loop12, that may be activated by an actuator (not shown) on the proximal end54 of the catheter 52.

Turning to FIGS. 4A-4D, a method for implanting the biosensor device 10in conjunction with a prosthesis 20 is shown. In a preferred method, theprosthesis 20 is implanted across an aneurysm 100 in an abdominal aorta102 of a patient with the biosensor device 10 secured around theprosthesis 20 such that the biosensor 14 is disposed within ananeurysmal sac 104 of the aneurysm 100. Alternatively, the method may beused to treat other enlarged or weakened regions within a blood vessel,for example, an aneurysm within the iliac arteries, the thoracic aorta,the cranial artery, and the like.

As shown in FIG. 4A, a guidewire 110 may be placed across the aneurysmsite 100 in a conventional manner, for example, from a peripheralartery, such as the femoral artery (not shown). The biosensor device 10,secured to the distal end 56 of the catheter 52, may be advancedendolumenally to the aneurysm site 100, for example, from thecontralateral femoral artery (not shown). Alternatively, the biosensordevice 10 may be advanced to the aneurysm site 100 from the sameperipheral artery as the guidewire 110 (not shown).

If constrained to the catheter 52, the loop 12 may be released from theconstraint (e.g., by withdrawing an overlying sheath) such that itextends substantially transversely across the aneurysm site 100. If theloop 12 is biased to its open configuration, the loop 12 mayautomatically unfurl or expand after being released to extend across theaneurysm site 100. Otherwise, the loop 12 may be manipulated to properlyorient it, for example, under fluoroscopic guidance, which may befacilitated by radiopaque markers (not shown) provided at predeterminedlocations on the loop 12.

Preferably, the loop 12 is manipulated such that it extends coaxiallyaround the guidewire 110. If the biosensor device 10 is introducedthrough the ipsilateral artery, the loop 12 may be aligned around theguidewire 110 before the biosensor device 10 is advanced to the aneurysmsite 100.

As shown in FIG. 4B, the prosthesis 20, in its contracted condition, maybe advanced endolumenally to the aneurysm site 100. For example, theprosthesis 20 may be secured to a delivery device 82, which may includea catheter, a sheath, and/or other conventional device, that may beadvanced over the guidewire 100. The prosthesis 20 may be positionedwith respect to the loop 12, for example, by advancing the deliverydevice 82 through the loop 12, and positioning the prosthesis 20 withrespect to the aneurysm 100.

This may also be performed under fluoroscopic guidance, with radiopaquemarkers provided on the delivery device 82 and/or on the prosthesis 20.Preferably, the prosthesis 20 is positioned such that ends 26, 28 of theprosthesis 20 are aligned with the healthy regions 106, 108 of thevessel adjacent to the aneurysm 100. The loop 12 may then be adjusted toposition it with respect to the prosthesis 20, i.e., to position thebiosensor 14 at a desired location along the length and/or around theouter surface of the prosthesis 20.

As shown in FIG. 4C, the prosthesis 20 may then be expanded to itsenlarged condition, thereby securing the ends 26, 28 to the healthyregions 106, 108 of the vessel, and substantially securing the loop 12around the prosthesis 20. For example, if the prosthesis 20 includes aself-expanding support structure, the prosthesis 20 may automaticallyexpand upon being released from the delivery device 82. Alternatively,an expandable member, such as a balloon (not shown) on the deliverydevice 82, may be used to forcibly expand the prosthesis 20, as is knownin the art. A final inflation of the balloon may be used to provide agood seal between the distal ends 26, 28 of the prosthesis 20 and thehealthy regions 106, 108 of the vessel.

Finally, as shown in FIG. 4D, the biosensor device 10 may be releasedfrom the catheter 52, and the catheter 52 and delivery apparatus 82withdrawn from the patient. Thus, the prosthesis 20 may be used tosubstantially isolate the aneurysm 100 from the rest of the bloodvessel. The biosensor 14 may then be used to monitor physiologicalconditions of the patient, such as pressure within the aneurysmal sac102, after implantation of the prosthesis 20. The biosensor 14 may beactivated remotely to provide pressure or other data, and therebyfacilitate monitoring the condition of an aneurysm to detect early signsof leaks or other potential problems.

In an alternative embodiment, the prosthesis 20, mounted to the deliverydevice 82 in its contracted condition, may be advanced to the aneurysmsite 100 over the guidewire 110 before the biosensor device 10 isintroduced therein (not shown). The biosensor device 10 may then beadvanced into the aneurysm site 100, as described above, and thenpositioned around the prosthesis 20 before the prosthesis 20 is expandedtowards its enlarged condition.

Alternatively, the loop 12 may be oriented around the delivery device 82at its proximal end (not shown) and the biosensor device 10 advanceddistally over the delivery device 82 using the catheter 52 until thebiosensor device 10 is positioned over the prosthesis 20 at the aneurysmsite 100. The prosthesis 20 may then be expanded, and the biosensordevice 10 released, as described above.

While the invention is susceptible to various modifications, andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formsor methods disclosed, but to the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the appended claims.

What is claimed is:
 1. A method for implanting a biosensor at atreatment site within a body lumen of a patient, comprising: advancing atubular prosthesis in a contracted state within the body lumen to thetreatment site; advancing a substantially enclosed loop to the treatmentsite, the loop including a biosensor attached thereto; positioning theloop and the prosthesis coaxially with respect to one another at thetreatment site; and expanding the prosthesis towards an enlargedcondition, thereby substantially engaging the loop around the prosthesisand substantially engaging the prosthesis with a wall of the bloodvessel at the treatment site.
 2. The method of claim 1, wherein the loopis advanced to the treatment site within a lumen of a deliveryapparatus, the loop being detachably secured to the delivery apparatus.3. The method of claim 2, further comprising deploying the loop from thedelivery apparatus before positioning the loop around the prosthesis. 4.The method of claim 3, further comprising releasing the loop from thedelivery apparatus after positioning the loop around the prosthesis. 5.The method of claim 4, wherein the loop is released from the deliverydevice after the prosthesis is expanded towards its enlarged condition.6. The method of claim 1, wherein the step of positioning the loopcomprises: expanding the loop across the treatment site before theprosthesis is advanced to the treatment site; and advancing theprosthesis through the loop upon advancement of the prosthesis to thetreatment site.
 7. The method of claim 1, wherein the prosthesis isadvanced to the treatment site mounted to a distal end of a deliverydevice, and wherein the loop is advanced coaxially over the deliverydevice to the treatment site.
 8. The method of claim 1, wherein thetreatment site comprises an aneurysm.
 9. The method of claim 8, whereinthe biosensor is disposed within an aneurysmal sac at least partiallydefined by the aneurysm after the prosthesis is expanded to its enlargedcondition.
 10. An apparatus for delivering a biosensor to a treatmentsite within a body lumen, comprising: a catheter having a proximal endand a distal end adapted for introduction into the body lumen; anattachment loop having a biosensor attached thereto; and a connector onthe distal end of the catheter for detachably securing the attachmentloop to the catheter, said connector comprising a wire extending throughthe catheter, the wire having a distal portion at the distal end of thecatheter that is intertwined with the attachment loop to substantiallysecure the loop to the distal end of the catheter.
 11. The apparatus ofclaim 10, further comprising an actuator on the proximal end of thecatheter for detaching the attachment loop from the connector.
 12. Theapparatus of claim 11, wherein the actuator comprises a handle on afirst end of the wire disposed at the proximal end of the catheter, thehandle configured for pulling the distal portion of the wire from thedistal end of the catheter towards the proximal end, thereby releasingthe attachment loop therefrom.
 13. The apparatus of claim 10, whereinthe attachment loop comprises a ring attached thereto for receiving thewire therethrough.
 14. The apparatus of claim 10, further comprising: atubular prosthesis expandable between a contracted condition forfacilitating introduction into the body lumen, and an enlarged conditionfor contacting a wall of the body lumen at the treatment site; and adelivery device for directing the prosthesis to the treatment site inits contracted condition, the delivery device having a cross-sectionsubstantially smaller than a cross-section of the attachment loop,thereby facilitating positioning the loop coaxially with respect to theprosthesis before the prosthesis is deployed from the delivery device.15. The apparatus of claim 14, wherein the attachment loop has a sizefor substantially securing the loop to the prosthesis in its enlargedcondition.
 16. The apparatus of claim 14, wherein the attachment loopcomprises a ring or sleeve formed from a substantially elastic material,the ring or sleeve having a relaxed state having a cross-section smallerthan the prosthesis in its enlarged condition.
 17. The apparatus ofclaim 14, wherein the attachment loop comprises a substantiallyinelastic thread having a cross-section similar to the prosthesis in itsenlarged condition.
 18. The apparatus of claim 10, further comprising asheath slidable over the catheter, the sheath being configured forreceiving the attachment loop therein.
 19. The apparatus of claim 18,wherein the attachment loop is biased to assume an open configurationupon release from the sheath.
 20. An apparatus for delivering abiosensor to a treatment site within a body lumen, comprising: acatheter having a proximal end and a distal end adapted for introductioninto the body lumen; an attachment loop having a biosensor attachedthereto, said biosensor extending radially outward from the loop; and aconnector on the distal end of the catheter for detachably securing theattachment loop to the catheter.
 21. The apparatus of claim 20, furthercomprising an actuator on the proximal end of the catheter for detachingthe attachment loop from the connector.
 22. The apparatus of claim 21,wherein the connector comprises a wire extending through the catheter,the wire having a distal portion at the distal end of the catheter thatis intertwined with the attachment loop to substantially secure theattachment loop to the distal end of the catheter.
 23. The apparatus ofclaim 22, wherein the actuator comprises a handle on a first end of thewire disposed at the proximal end of the catheter, the handle configuredfor pulling the distal portion of the wire from the distal end of thecatheter towards the proximal end, thereby releasing the attachment looptherefrom.
 24. The apparatus of claim 22, wherein the attachment loopcomprises a ring attached thereto for receiving the wire therethrough.25. The apparatus of claim 20, further comprising: a tubular prosthesisexpandable between a contracted condition for facilitating introductioninto the body lumen, and an enlarged condition for contacting a wall ofthe body lumen at the treatment site; and a delivery device fordirecting the prosthesis to the treatment site in its contractedcondition, the delivery device having a cross-section substantiallysmaller than a cross-section of the attachment loop, therebyfacilitating positioning the attachment loop coaxially with respect tothe prosthesis before the prosthesis is deployed from the deliverydevice.
 26. The apparatus of claim 25, wherein the attachment loop has asize for substantially securing the attachment loop to the prosthesis inits enlarged condition.
 27. The apparatus of claim 25, wherein theattachment loop comprises a ring or sleeve formed from a substantiallyelastic material, the ring or sleeve having a relaxed state having across-section smaller than the prosthesis in its enlarged condition. 28.The apparatus of claim 25, wherein the attachment loop comprises asubstantially inelastic thread having a cross-section similar to theprosthesis in its enlarged condition.
 29. The apparatus of claim 20,further comprising a sheath slidable over the catheter, the sheath beingconfigured for receiving the attachment loop therein.
 30. The apparatusof claim 29, wherein the attachment loop is biased to assume an openconfiguration upon release from the sheath.
 31. An apparatus formonitoring a physical parameter at an aneurysmal site within a bloodvessel lumen comprising: a tubular prosthesis expandable between acontracted condition for facilitating introduction of the prosthesisinto the lumen of the blood vessel, and an enlarged condition forcontacting a wall of the blood vessel lumen; a substantially enclosedattachment loop having a size for securing the attachment loop coaxiallyaround the prosthesis in its enlarged condition; and a biosensorattached to the attachment loop and extending radially outward from theattachment loop for positioning the biosensor within an aneurysmal sac.32. The apparatus of claim 31, wherein the biosensor is a sensorselected from the group consisting of a pressure sensor, a temperaturesensor, a pH sensor, a blood sugar sensor, a blood oxygen sensor, amotion sensor, an acceleration sensor, a force sensor, a strain sensor,an acoustics sensor, a moisture sensor, an osmolarity sensor, a lightsensor, a turbidity sensor, a radiation sensor, an electromagnetic fieldsensor, a chemical sensor, an ionic sensor, and an enzymatic sensor. 33.An apparatus for use with a tubular prosthesis in monitoring a physicalparameter at a site within a body lumen, comprising: a substantiallyenclosed attachment loop configured for attachment to an outercircumference of the prosthesis; and a biosensor attached to theattachment loop, said biosensor extending radially outward from theattachment loop.
 34. The apparatus of claim 33, wherein the attachmentloop comprises a ring or sleeve formed from a substantially elasticmaterial, the ring or sleeve having a relaxed state having across-section smaller than the prosthesis in an enlarged condition. 35.The apparatus of claim 34, wherein the elastic material has anelasticity such that the ring or sleeve applies a radially inwardpressure of between about 5-60 mm Hg against the prosthesis in anenlarged condition when the ring or sleeve is substantially securedthereto.
 36. The apparatus of claim 33, wherein the attachment loopcomprises a substantially inelastic thread having a cross-sectionsimilar to the prosthesis in an enlarged condition.
 37. The apparatus ofclaim 36, wherein the thread has a cross-section about 5-30 percentlarger than a cross-section of the prosthesis in an enlarged condition.38. The apparatus of claim 33, wherein the attachment loop is biased toassume a substantially open configuration.
 39. The apparatus of claim33, wherein the attachment loop is compressible to facilitate itsinsertion into a delivery device.
 40. The apparatus of claim 33, whereinthe attachment loop comprises a connector thereon for cooperating with amating connector on a device for delivering the attachment loop withinthe body lumen.
 41. The apparatus of claim 33, wherein the biosensor isa sensor selected from the group consisting of a pressure sensor, atemperature sensor, a pH sensor, a blood sugar sensor, a blood oxygensensor, a motion sensor, a flow sensor, a velocity sensor, anacceleration sensor, a force sensor, a strain sensor, an acousticssensor, a moisture sensor, an osmolarity sensor, a light sensor, aturbidity sensor, a radiation sensor, an electromagnetic field sensor, achemical sensor, an ionic sensor, and an enzymatic sensor.